reliability of track reconstruction inthe high-multiplicity envi- ronment of heavy-ion collisions, more stringent requirements on track quality, compared to those deﬁned for proton-proton collisions , are used. At least nine hits inthe silicon detectors (out of a typical value of 11) are required for each track, with no missing pixel hits and not more than one missing SCT hit, in both cases where such hits are expected. In addition, the point of closest approach is required to be within 1 mm ofthe primary vertex in both the transverse and the longitudinal directions . This selection is varied inthe analysis to check the inﬂuence of both the acceptance and fake tracks. The tracking efﬁciency forcharged particles is studied by comparing data to Monte Carlo calculations based on the HIJING event generator  and a full GEANT 4  simulation ofthedetector. This efﬁciency is estimated to be about 72% near midrapidity in central events. However, this analysis is found to be insensitive to variations inthe tracking efﬁciency, as found previously . Fake tracks from random combinations of hits are generally negligible, reaching only 0.1% for | η | < 1 forthe highest multiplicity events. This rate increases slightly at large η.
had p T exceeding 4 GeV, the event was accepted for further processing by the high-level trigger (HLT). The L1 muon algorithm also identified regions of interest (RoI) within thedetector to be investigated by the HLT. Inthe HLT, the track parameters of each muon were recalculated by including the precision data from the MDT or CSC inthe RoI defined by the previous trigger level. Muon candidates were reconstructed either solely from the MS or using combined data from the MS and ID. In addition to the events selected using the RoI-based muon trigger, the reconstruction was performed over the whole MS by the HLT to identify muons with p T > 10 GeV. The full scan searched all events in which a neutral particle signal was detected in each of two zero degree calorimeters (ZDC) ( jj > 8:3 ), or which contained an energy deposi- tion inthe calorimeters of E T > 10 GeV .
Thecharged-particle reconstruction eﬃciency, ε ( p T , η ) , was evaluated separately in each ofthe seven centrality bins used in this analysis for truth particles within R = 0 . 4 of R = 0 . 4 truth jets having p T jet true > 100 GeV. Fig. 2 shows the eﬃciency as a function of truth-particle p T averaged over | η | < 1 (top) and 1 < | η | < 2 . 5 (bottom) forthe 0–10% and 60–80% centrality bins. For p T < 8 GeV, ε ( p T , η ) was directly evaluated using ﬁne bins in p T and η . For p T > 8 GeV the p T dependence ofthe eﬃciencies were parameterized separately inthe two pseudorapidity intervals shown in Fig. 2 using a functional form that describes trends at low p T as well as at high p T . An example ofthe resulting param- eterizations is shown by the solid curves in Fig. 2. A centrality- dependent systematic uncertainty inthe parameterized eﬃcien- cies, shown by the shaded bands in Fig. 2, was evaluated based on both the uncertainties inthe parameterization and on observed variations ofthe eﬃciency with p T , which largely result from loss of hits inthe SCT at higher detector occupancy. Thus, the system- atic uncertainty inthe 60–80% centrality bin is small because no signiﬁcant variation ofthe eﬃciency is observed at low detector occupancy, while the uncertainties are largest forthe 0–10% cen- trality bin withthe largest detector occupancies.
The interpretation ofthe long-range correlations in high-multiplicity p+p and p+Pb collisions is currently a subject of intense study. References [29–32] argue that the produced matter in these collisions is sufficiently voluminous and dense such that the hydrodynamic model framework may still apply. On the other hand, models based on gluon saturation and color connections suggest that the long-range correlations are an initial-state effect, intrinsic to QCD at high gluon density [33–37]. Recently a hybrid model that takes into account both the initial- and final-state effects has been proposed . All these approaches can describe, qualitatively and even quantitatively, the v 2 and v 3 data
origin at the nominal interaction point (IP) inthe centre ofthedetector and the z-axis along the beam pipe. The x-axis points from the IP to the centre ofthe LHC ring, and the y-axis points upward. Cylindrical coordinates (r, φ) are used inthe transverse plane, φ being theazimuthal angle around the beam pipe. Forthe p+Pb collisions, the incident Pb beam travelled inthe +z direction. The pseudorapidity is defined in laboratory coordinates in terms ofthe polar angle θ as η = − ln tan(θ/2). Transverse momentum and energy are defined as p T = p sinθ and E T = E sinθ, respectively.
A. Olariu 26a , A. G. Olchevski 64 , S. A. Olivares Pino 46 , D. Oliveira Damazio 25 , E. Oliver Garcia 168 , A. Olszewski 39 , J. Olszowska 39 , A. Onofre 125a,125e , P. U. E. Onyisi 31,o , C. J. Oram 160a , M. J. Oreglia 31 , Y. Oren 154 , D. Orestano 135a,135b , N. Orlando 72a,72b , C. Oropeza Barrera 53 , R. S. Orr 159 , B. Osculati 50a,50b , R. Ospanov 121 , G. Otero y Garzon 27 , H. Otono 69 , M. Ouchrif 136d , E. A. Ouellette 170 , F. Ould-Saada 118 , A. Ouraou 137 , K. P. Oussoren 106 , Q. Ouyang 33a , A. Ovcharova 15 , M. Owen 83 , V. E. Ozcan 19a , N. Ozturk 8 , K. Pachal 119 , A. Pacheco Pages 12 , C. Padilla Aranda 12 , M. Pagáˇcová 48 , S. Pagan Griso 15 , E. Paganis 140 , C. Pahl 100 , F. Paige 25 , P. Pais 85 , K. Pajchel 118 , G. Palacino 160b , S. Palestini 30 , M. Palka 38b , D. Pallin 34 , A. Palma 125a,125b , J. D. Palmer 18 , Y. B. Pan 174 , E. Panagiotopoulou 10 , J. G. Panduro Vazquez 76 , P. Pani 106 , N. Panikashvili 88 , S. Panitkin 25 , D. Pantea 26a , L. Paolozzi 134a,134b , Th. D. Papadopoulou 10 , K. Papageorgiou 155,l , A. Paramonov 6 , D. Paredes Hernandez 34 , M. A. Parker 28 , F. Parodi 50a,50b , J. A. Parsons 35 , U. Parzefall 48 , E. Pasqualucci 133a , S. Passaggio 50a , A. Passeri 135a , F. Pastore 135a,135b,* , Fr. Pastore 76 , G. Pásztor 29 , S. Pataraia 176 , N. D. Patel 151 , J. R. Pater 83 , S. Patricelli 103a,103b , T. Pauly 30 , J. Pearce 170 , M. Pedersen 118 , S. Pedraza Lopez 168 , R. Pedro 125a,125b , S. V. Peleganchuk 108 , D. Pelikan 167 , H. Peng 33b , B. Penning 31 , J. Penwell 60 , D. V. Perepelitsa 25 , E. Perez Codina 160a , M. T. Pérez García-Estañ 168 , V. Perez Reale 35 , L. Perini 90a,90b , H. Pernegger 30 , R. Perrino 72a , R. Peschke 42 , V. D. Peshekhonov 64 , K. Peters 30 , R. F. Y. Peters 83 , B. A. Petersen 30 , T. C. Petersen 36 , E. Petit 42 , A. Petridis 147a,147b , C. Petridou 155 , E. Petrolo 133a , F. Petrucci 135a,135b , N. E. Pettersson 158 , R. Pezoa 32b , P. W. Phillips 130 , G. Piacquadio 144 , E. Pianori 171 , A. Picazio 49 , E. Piccaro 75 , M. Piccinini 20a,20b , R. Piegaia 27 , D. T. Pignotti 110 , J. E. Pilcher 31 , A. D. Pilkington 77 , J. Pina 125a,125b,125d , M. Pinamonti 165a,165c,ac , A. Pinder 119 , J. L. Pinfold 3 , A. Pingel 36 , B. Pinto 125a , S. Pires 79 , M. Pitt 173 , C. Pizio 90a,90b , L. Plazak 145a , M.-A. Pleier 25 , V. Pleskot 128 , E. Plotnikova 64 , P. Plucinski 147a,147b , S. Poddar 58a , F. Podlyski 34 , R. Poettgen 82 , L. Poggioli 116 , D. Pohl 21 , M. Pohl 49 , G. Polesello 120a , A. Policicchio 37a,37b , R. Polifka 159 , A. Polini 20a , C. S. Pollard 45 , V. Polychronakos 25 , K. Pommès 30 , L. Pontecorvo 133a , B. G. Pope 89 , G. A. Popeneciu 26b , D. S. Popovic 13a , A. Poppleton 30 , X. Portell Bueso 12 , S. Pospisil 127 , K. Potamianos 15 , I. N. Potrap 64 , C. J. Potter 150 , C. T. Potter 115 , G. Poulard 30 , J. Poveda 60 , V. Pozdnyakov 64 , P. Pralavorio 84 , A. Pranko 15 ,
F. Ledroit-Guillon 55 , C.A. Lee 152 , H. Lee 106 , J.S.H. Lee 117 , S.C. Lee 152 , L. Lee 177 , G. Lefebvre 79 , M. Lefebvre 170 , F. Legger 99 , C. Leggett 15 , A. Lehan 73 , M. Lehmacher 21 , G. Lehmann Miotto 30 , X. Lei 7 , W.A. Leight 29 , A. Leisos 155 , A.G. Leister 177 , M.A.L. Leite 24d , R. Leitner 128 , D. Lellouch 173 , B. Lemmer 54 , K.J.C. Leney 77 , T. Lenz 21 , G. Lenzen 176 , B. Lenzi 30 , R. Leone 7 , S. Leone 123a,123b , K. Leonhardt 44 , C. Leonidopoulos 46 , S. Leontsinis 10 , C. Leroy 94 , C.G. Lester 28 , C.M. Lester 121 , M. Levchenko 122 , J. Levêque 5 , D. Levin 88 , L.J. Levinson 173 , M. Levy 18 , A. Lewis 119 , G.H. Lewis 109 , A.M. Leyko 21 , M. Leyton 41 , B. Li 33b,u , B. Li 84 , H. Li 149 , H.L. Li 31 , L. Li 45 , L. Li 33e , S. Li 45 , Y. Li 33c,v , Z. Liang 138 , H. Liao 34 , B. Liberti 134a , P. Lichard 30 , K. Lie 166 , J. Liebal 21 , W. Liebig 14 , C. Limbach 21 , A. Limosani 87 , S.C. Lin 152,w , T.H. Lin 82 , F. Linde 106 , B.E. Lindquist 149 , J.T. Linnemann 89 , E. Lipeles 121 , A. Lipniacka 14 , M. Lisovyi 42 , T.M. Liss 166 , D. Lissauer 25 , A. Lister 169 , A.M. Litke 138 , B. Liu 152 , D. Liu 152 , J.B. Liu 33b , K. Liu 33b,x , L. Liu 88 , M. Liu 45 , M. Liu 33b , Y. Liu 33b , M. Livan 120a,120b , S.S.A. Livermore 119 , A. Lleres 55 , J. Llorente Merino 81 , S.L. Lloyd 75 , F. Lo Sterzo 152 , E. Lobodzinska 42 , P. Loch 7 , W.S. Lockman 138 , T. Loddenkoetter 21 , F.K. Loebinger 83 , A.E. Loevschall-Jensen 36 , A. Loginov 177 , T. Lohse 16 , K. Lohwasser 42 , M. Lokajicek 126 , V.P. Lombardo 5 , B.A. Long 22 , J.D. Long 88 , R.E. Long 71 , L. Lopes 125a , D. Lopez Mateos 57 , B. Lopez Paredes 140 , I. Lopez Paz 12 , J. Lorenz 99 , N. Lorenzo Martinez 60 , M. Losada 163 ,
origin at the nominal interaction point (IP) inthe cen- ter ofthedetector and the z-axis along the beam pipe. The x-axis points from the IP to the center ofthe LHC ring, and the y-axis points upward. Cylindrical coordi- nates (r, φ) are used inthe transverse plane, φ being theazimuthal angle around the beam pipe. Forthe p+Pb col- lisions, the incident Pb beam traveled inthe +z direction. The pseudorapidity is defined in laboratory coordinates in terms ofthe polar angle θ as η = − ln tan(θ/2).  ATLAS Collaboration, JINST 3 , S08003 (2008).  ATLAS Collaboration, Eur. Phys. J. C70 , 787 (2010).  ATLAS Collaboration, New J. Phys. 13 , 053033 (2011).  X.-N. Wang and M. Gyulassy, Phys. Rev. D 44 , 3501
The systematic uncertainties associated withthe analysis procedure are dominated by contributions from residual detector acceptance effects and uncertainties inthe resolution factors. Most detector acceptance effects are expected to cancel inthe raw correlation function by dividing the foreground and background distributions [Eqs. (18)–(20)]. The residual accep- tance effects, estimated by the sine terms ofthe distributions, are found to be (0 . 2–1 . 5) × 10 −3 ofthe average amplitude ofthe correlation functions and are found to be independent ofthe event centrality. The uncertainties inthe resolution factors are calculated from the differences between the 2SE estimate and various 3SE estimates, which are then propagated to give the total uncertainties forthe combined resolution factor. These uncertainties are found to be quite similar inthe EP and SP methods because they both rely on the same subevent correlations; the larger ofthe two is quoted as the total systematic uncertainty. The uncorrelated uncertainties are evaluated separately via Eq. (21) and are used for comparison between the two methods. The uncertainties inthe resolution factors are found to depend only weakly on event centrality.
The trigger system has three stages, the ﬁrst of which (Level-1) is hardware-based, while the later stages (Level-2 and Event Fil- ter ) are based on software algorithms. The minimum-bias Level-1 trigger used for this analysis requires signals in either the two sets of minimum-bias trigger scintillator (MBTS) counters, cov- ering 2 . 1 < | η | < 3 . 9 on each side ofthe experiment, or the two zero-degree calorimeters (ZDC), each positioned at | z | = 140 m rel- ative to the centre ofthedetector, detecting neutrons and photons with | η | > 8 . 3. The ZDC Level-1 trigger thresholds were set just below the single neutron peak on each side. The MBTS trigger was conﬁgured to require at least one hit above threshold from each side ofthedetector. A Level-2 timing requirement on signals from the MBTS was then imposed to remove beam backgrounds, while the ZDC had no further requirements beyond the Level-1 decision. The Event Filter was not needed forthe minimum-bias triggering and was run in pass-through mode.
S. Donati 123a,123b , P. Dondero 120a,120b , J. Donini 34 , J. Dopke 30 , A. Doria 103a , M. T. Dova 70 , A. T. Doyle 53 , M. Dris 10 , J. Dubbert 88 , S. Dube 15 , E. Dubreuil 34 , E. Duchovni 173 , G. Duckeck 99 , O. A. Ducu 26a , D. Duda 176 , A. Dudarev 30 , F. Dudziak 63 , L. Duflot 116 , L. Duguid 76 , M. Dührssen 30 , M. Dunford 58a , H. Duran Yildiz 4a , M. Düren 52 , A. Durglishvili 51b , M. Dwuznik 38a , M. Dyndal 38a , J. Ebke 99 , W. Edson 2 , N. C. Edwards 46 , W. Ehrenfeld 21 , T. Eifert 144 , G. Eigen 14 , K. Einsweiler 15 , T. Ekelof 167 , M. El Kacimi 136c , M. Ellert 167 , S. Elles 5 , F. Ellinghaus 82 , N. Ellis 30 , J. Elmsheuser 99 , M. Elsing 30 , D. Emeliyanov 130 , Y. Enari 156 , O. C. Endner 82 , M. Endo 117 , R. Engelmann 149 , J. Erdmann 177 , A. Ereditato 17 , D. Eriksson 147a , G. Ernis 176 , J. Ernst 2 , M. Ernst 25 , J. Ernwein 137 , D. Errede 166 , S. Errede 166 , E. Ertel 82 , M. Escalier 116 , H. Esch 43 , C. Escobar 124 , B. Esposito 47 , A. I. Etienvre 137 , E. Etzion 154 , H. Evans 60 , L. Fabbri 20a ,20b , G. Facini 30 , R. M. Fakhrutdinov 129 , S. Falciano 133a , J. Faltova 128 , Y. Fang 33a , M. Fanti 90a,90b , A. Farbin 8 , A. Farilla 135a , T. Farooque 12 , S. Farrell 164 , S. M. Farrington 171 , P. Farthouat 30 , F. Fassi 168 , P. Fassnacht 30 , D. Fassouliotis 9 , A. Favareto 50a,50b , L. Fayard 116 , P. Federic 145a , O. L. Fedin 122,i , W. Fedorko 169 , M. Fehling-Kaschek 48 , S. Feigl 30 , L. Feligioni 84 , C. Feng 33d , E. J. Feng 6 , H. Feng 88 , A. B. Fenyuk 129 , S. Fernandez Perez 30 , S. Ferrag 53 , J. Ferrando 53 , A. Ferrari 167 , P. Ferrari 106 , R. Ferrari 120a , D. E. Ferreira de Lima 53 , A. Ferrer 168 , D. Ferrere 49 , C. Ferretti 88 , A. Ferretto Parodi 50a,50b , M. Fiascaris 31 , F. Fiedler 82 , A. Filipˇciˇc 74 , M. Filipuzzi 42 , F. Filthaut 105 , M. Fincke- Keeler 170 , K. D. Finelli 151 , M. C. N. Fiolhais 125a,125c , L. Fiorini 168 , A. Firan 40 , J. Fischer 176 , W. C. Fisher 89 , E. A. Fitzgerald
The data forthe measurements presented here were collected with a minimum-bias trigger. This required a coincidence in either the two minimum- bias trigger scintillator (MBTS) detectors, located at ±3.56 m from the inter- action centre and covering 2.1 < |η| < 3.9, or two zero-degree calorimeters (ZDCs), located at ±140 m from the interaction centre and covering |η| > 8.3. The threshold on the analog energy sum in each ZDC was set below the sin- gle neutron peak. The offline analysis required the time difference between the two MBTS detectors to be |∆t| < 3 ns to eliminate upstream beam-gas inter- actions, a ZDC coincidence to efficiently reject photo-nuclear events , and a reconstructed vertex satisfying the selection described above. The measure- ments presented in this paper were obtained from a 10 hour data-taking run corresponding to an integrated luminosity of approximately 480 mb −1 . A total of 1631525 events passed the trigger, vertex, and offline selections.
Heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) create hot, dense matter that is thought to be composed of strongly in- teracting quarks and gluons. A useful tool to study the properties of this matter is theazimuthalanisotropyofparticle emission inthe transverse plane [1, 2]. This anisotropy has been interpreted as a result of pressure-driven anisotropic expansion (referred to as “flow”) ofthe created matter, and is described by a Fourier expansion oftheparticle distribution inazimuthal angle φ, around the beam direction:
Liquid argon technology providing excellent energy and position resolution is used inthe electromagnetic calorime- ter that covers the pseudorapidity range jj < 3:2 . The hadronic calorimetry inthe range jj < 1:7 is provided by a sampling calorimeter made of steel and scintillating tiles. Inthe end caps ( 1:5 < jj < 3:2 ), liquid argon tech- nology is also used forthe hadronic calorimeters, matching the outer jj limits ofthe electromagnetic calorimeters. To complete the coverage, the liquid argon forward calo- rimeters provide both electromagnetic and hadronic energy measurements, extending the coverage up to jj ¼ 4:9 . The calorimeter ( and ) granularities are 0:1 0:1 forthe hadronic calorimeters up to jj ¼ 2:5 (except forthe third layer ofthe tile calorimeter, which has a segmentation of 0:2 0:1 up to jj ¼ 1:7 ) and then 0:2 0:2 up to jj ¼ 4:9 . The electromagnetic calorimeters are longitudi- nally segmented into three compartments and feature a much finer readout granularity varying by layer, with cells as small as 0:025 0:025 extending to jj ¼ 2:5 inthe middle layer. Inthe data-taking period considered, ap- proximately 187 000 calorimeter cells (98% ofthe total) were usable for event reconstruction.
The measurements presented here were performed withtheATLASdetector  using its calorimeter, inner detec- tor, trigger, and data acquisition systems. The calorimeter system consists of a liquid-argon electromagnetic (EM) calorimeter covering jj < 3:2 , a steel-scintillator sampling hadronic calorimeter covering jj < 1:7 , a liquid-argon hadronic calorimeter covering 1:5 < jj < 3:2, and a forward calorimeter (FCal) covering 3:2 < jj < 4:9 . Charged-particle tracks were measured over the range jj < 2:5 using the inner detector , which is composed of silicon pixel detectors inthe innermost layers, followed by silicon microstrip detectors and a straw-tube transition- radiation tracker ( jj < 2:0 ), all immersed in a 2 T axial magnetic field. The zero-degree calorimeters (ZDCs) are located symmetrically at z ¼ 140 m and cover jj > 8:3 . In Pb þ Pb collisionsthe ZDCs primarily mea- sure noninteracting ‘‘spectator’’ neutrons from the incident nuclei. A ZDC coincidence trigger was defined by requiring a signal consistent with one or more neutrons in each ofthe calorimeters.
To further understand the discrepancies between the mea- surement and the MC predictions, studies ofthe effects of various sources of systematic uncertainty inthe MC predic- tions are carried out using the POWHEG+PYTHIA MC pro- gram. The uncertainties on the calculated R are evaluated by varying independently the renormalization and factori- zation scales between 0.5 and 2 times the default scale. The largest shift of R with respect to the default calculation is taken as the corresponding systematic error due to the un- certainties ofthe renormalization and factorization scales. Similarly the possible systematic uncertainties associated withthe charm and bottom quark masses are estimated by varying them independently within 0 : 2 GeV and 0 : 25 GeV, respectively. The systematic uncertainties due to fðc ! D þ Þ and fðb ! D þ XÞ are evaluated by changing their values according to their measured uncer- tainties [37–42]. Contributions from other sources, such as the value ofthe strong coupling constant and the uncertainty ofthe parton density function ofthe proton are much smaller and they are not taken into account. The total systematic uncertainty ofthe MC calculations is computed by summing each individual systematic uncertainty in quadrature. As shown in Fig. 4, although the predicted values of R have sizable systematic uncertainties in each bin, especially for large p T and z , the systematic errors become much smaller
systematic uncertainty comes from the knowledge ofthe upstream material. A dedicated simulated sample that includes additional material inthe inner detector and in front ofthe electromagnetic calorimeter was used to assess the impact of a different account of material budget on the photon identification efficiency. The resulting uncertainty on ε ID γ is 6.3% (7.5%) for photons inthe range |η| < 1.8 (|η| > 1.8). Other sources of uncertainty arise from the simple shift approximation forthe data/simulation corrections (3%), from the discriminating variable distribution bias due to background contamination inthe W γ photon candidate data sample (4%), and from inefficiencies inthe reconstruction of photon conversions (2%). Since only prompt photons are present inthe W γ and Zγ MC samples, the efficiency ofthe fragmentation photon component is calculated using an alpgen  “W + 1 jet” fully simulated sample by selecting events with a high E T photon produced in
We thank CERN forthe very successful operation ofthe LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of ANPCyT, Argentina; YerPhI, Armenia; ARC, Australia; BMWF, Austria; ANAS, Azerbaijan; SSTC, Belarus; CNPq and FAPESP, Brazil; NSERC, NRC and CFI, Canada; CERN; CONICYT, Chile; CAS, MOST and NSFC, China; COLCIENCIAS, Colombia; MSMT CR, MPO CR and VSC CR, Czech Republic; DNRF, DNSRC and Lundbeck Foundation, Denmark; ARTEMIS, European Union; IN2P3-CNRS, CEA-DSM/IRFU, France; GNAS, Georgia; BMBF, DFG, HGF, MPG and AvH Foundation, Germany; GSRT, Greece; ISF, MINERVA, GIF, DIP and Benoziyo Center, Israel; INFN, Italy; MEXT and JSPS, Japan; CNRST, Morocco; FOM and NWO, Netherlands; RCN, Norway; MNiSW, Poland; GRICES and FCT, Portugal; MERYS (MECTS), Romania; MES of Russia and ROSATOM, Russian Federation; JINR; MSTD, Serbia; MSSR, Slovakia; ARRS and MVZT, Slovenia; DST/NRF, South Africa; MICINN, Spain; SRC and Wallenberg Foundation, Sweden; SER, SNSF and Cantons of Bern and Geneva, Switzerland; NSC, Taiwan; TAEK, Turkey; STFC, the Royal Society and Leverhulme Trust, United Kingdom; DOE and NSF, United States of America. The crucial computing support from all WLCG partners is acknowledged gratefully, in particular, from CERN and theATLAS Tier-1 facilities at TRIUMF (Canada), NDGF (Denmark, Norway, Sweden), CC- IN2P3 (France), KIT/GridKA (Germany), INFN-CNAF (Italy), NL-T1 (Netherlands), PIC (Spain), ASGC (Taiwan), RAL (UK) and BNL (USA) and inthe Tier-2 facilities worldwide.
a cone of radius ∆R = 0.5; the small fraction of events with jets containing more than one muon is discarded. The soft-muon tagging (SMT) efficiency and mistagging rate are measured in data . The overall c-tagging efficiency is about 4%, due mainly to the low branching ratio of charmed hadrons to muons (approximately 10%). The light-quark mistagging efficiency is around 0.2% depending on the jet kinematics. Scale factors are applied to correct the MC simulation efficiencies to those measured in data. Efficiency scale factors are applied to b- and c-jets. Scale factors forthe mistagging rates are applied to light jets. Two additional requirements, with minor impact on the signal, are applied inthe muon channel to suppress the Z +jets and the Υ backgrounds. First, the c-jet candidate is required to have either a track multiplicity of at least three or an electromagnetic-to-total energy fraction of less than 0.8. Second, the event is discarded if the invariant mass ofthe soft muon and the muon from the decay ofthe W -boson candidate is close to either the Z-boson mass (i.e. 80–100 GeV) or the Υ mass (i.e. 8–11 GeV).